Conventionally, there has been known an electromagnetic suspension apparatus including an electromagnetic actuator which is provided in parallel with a spring member provided between a vehicle body and a wheel of a vehicle and generates a driving force related to vibration damping of the vehicle body by an electric motor (for example, see Japanese Patent Application Publication No. 2010-132222). The electromagnetic actuator is configured to include a ball screw mechanism in addition to the electric motor. The electromagnetic actuator operates to generate the driving force related to the vibration damping of the vehicle body by converting rotational motion of the electric motor into linear motion of the ball screw mechanism.
In the electromagnetic suspension apparatus according to Japanese Patent Application Publication No. 2010-132222, a frictional force is generated in an internal mechanism such as a ball screw mechanism. For example, when the vehicle starts in a low temperature environment, the frictional force is large because viscosity of grease present in the internal mechanism of the electromagnetic actuator is high. In this case, as a result of failing to appropriately transmit the driving force generated by the electromagnetic actuator to a sprung member and an unsprung member, ride comfort and steering stability may be deteriorated.
In order to solve problems derived from such a frictional force, in the electromagnetic actuator according to Japanese Patent Application Publication No. 2011-189774, the electric motor is driven by a preset friction measurement driving force at the start of the vehicle, the frictional force of the electromagnetic actuator is calculated from a rotation angle of the electric motor at this time, and a target driving force of the electromagnetic actuator is corrected based on the calculated frictional force. With the electromagnetic actuator according to Japanese Patent Application Publication No. 2011-189774, it is possible to eliminate a problem associated with insufficient transmission of driving force derived from the frictional force which is remarkably generated at the time of starting the vehicle.